A variety of manufacturing equipment have been utilized in the production of low density extruded polymeric foam materials. Many conventional manufacturing systems include a foam extrusion system having a horizontal vacuum chamber with an extrusion die positioned at one end of the vacuum chamber and an exit opening arranged at the opposite end of the vacuum chamber with a liquid baffle, typically water, used to seal the vacuum chamber. Other mechanisms may be included within the vacuum chamber for the formation and transport of the foam including, for example an extrusion die, sizing and measuring devices and rollers and/or other conveyors for directing the foam extrudate from the extrusion die, below the surface of the liquid baffle and through the exit opening.
The production of high quality, low density polystyrene foam board sold under the well known color PINK® and FOAMULAR® trademarks by Owens Corning of Toledo, Ohio, USA, has been accomplished using such inclined barometric leg vacuum extrusion lines. As noted above, a die is typically positioned within an upper portion of the vacuum chamber, along with shaping, tractor and/or calibration equipment to form and shape the foam extrudate that is then submerged in a pond and removed from the vacuum chamber through a submerged orifice into an atmospheric portion of the pond. The foam extrudate, which may be cooled by a combination of cooling air zones within the vacuum chamber and throughout the entire process length as well as its passage through the pond, may then be withdrawn from the pond for additional processing and/or cutting to commercial sizes. Such installations, however, are mechanically complex and, as a result, tend to be both costly and difficult to operate, particularly since the upper portion of the chamber may be a number of meters above and a substantial distance horizontally removed from the lower portion.
One such apparatus is disclosed in Pagan's U.S. Pat. No. 4,783,291 in which the liquid baffle included a pond of liquid that is maintained at a higher level within the vacuum chamber and at a lower level outside the chamber. The level of the liquid baffle within the vacuum chamber is formed between a dam plate and a seal plate arranged at the exit end of the vacuum chamber. As disclosed by Pagan, the seal plate includes a size adjustable window through which the foam extrudate passes as it is guided by a conveyor downwardly into the internal section of the pond, through an orifice provided in the seal plate or bulkhead and then upwardly through the external section of the pond using a conveyor that includes a large radius curved section.
Pagan also disclosed controlling the level of liquid in the vacuum chamber by circulating liquid from the internal section to the external section of the pond, with the amount of liquid circulated being inversely proportional to the absolute pressure maintained within the vacuum chamber. The sizing of the orifice through which the extrudate exits the vacuum chamber is controlled by a movable shutter arranged above the orifice and positioned in response to vacuum level. In this manner the shutter acts as a gross flow control valve for water tending to move from the atmospheric section of the pond into the vacuum section of the pond.
Another apparatus is disclosed in Lightle et al.'s U.S. Pat. No. 5,753,161 which disclosed a horizontal vacuum extrusion line including a fixed bulkhead, a die inside the bulkhead, a telescoping vacuum chamber section and a fixed chamber section. A dam was provided in the fixed chamber section to form a pond for immersion cooling of the extrudate. A truss was provided within the vacuum chamber and extended from the dam to the bulkhead and extending through the telescoping vacuum chamber section for supporting shaping and calibration equipment.
As disclosed in Lightle, the apparatus included fluid pressurizable seals arranged at each end of the telescoping vacuum section that were operable after the telescoping section is closed against the bulkhead and the telescoping and fixed sections are locked together. The use of the telescoping vacuum section allowed the construction of a more compact line and improved access to equipment arranged downstream of the extrusion die.
The extrudate from the die is directed down into the pond and then through an orifice in a hood projecting from the chamber into a lower level portion of the pond that extends outside of the vacuum chamber. The hood also included a tractor drive for pushing the extrudate through the underwater orifice and a means for controlling the higher level of the pond within the vacuum chamber downstream of the dam.
Another apparatus was disclosed in Sadinski's U.S. Pat. No. 6,116,882, which disclosed an extrusion system that could include single or tandem extruders and a mixer-cooler to extrude a foamable extrudate through a die arranged in a vacuum chamber. The mixer-cooler is utilized to achieve a narrow range of melt viscosity of the melt before the melt is extruded through the die. The extrudate was then shaped and calibrated within the vacuum chamber to produce a low density foamed product.
The extrudate is then removed from the vacuum chamber on a continuous basis through an orifice that is submerged in a water baffle immersion seal. The extrudate is directed to the submerged orifice with a free wheeling guiding system arranged upstream of the orifice with the configuration of the orifice continually adjusted to compensate for variations in the sizing of the extrudate. Before the extrudate passes into the water baffle seal it moves over a floating dancer roll, the position of which controls a haul-off device such as a vacuum belt arranged downstream of the orifice to avoid the need to push or otherwise drive the extrudate within the vacuum chamber.
Another apparatus was disclosed in Sadinski's U.S. Pat. No. 6,213,752, which disclosed a vacuum extrusion line that incorporated a vacuum chamber having an extrusion die at one end and a water baffle immersion cooler at the other end for extracting the extrudate to atmosphere. The vacuum chamber further included extrudate shaping and sizing equipment arranged downstream of the die, a large diameter fixed bulkhead, two large diameter movable sections surrounding the shaping and sizing equipment and a smaller fixed section of the chamber.
The position of both the first and second moveable sections may be adjusted to seal against the fixed section and/or the fixed bulkhead and complete the vacuum chamber or moved to open an access gap to aid in the servicing of the downstream equipment with a simplified lock mechanism that facilitates the opening and closing of the vacuum chamber.